View source for Apps-On-Physics/C2/Reflection-and-Refraction/English

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|| '''Visual Cue'''
|| '''Narration'''
|-
|| '''Slide Number 1'''

'''Title slide'''
|| Welcome to the Spoken Tutorial on '''Reflection and Refraction'''.
|-
|| '''Slide Number 2 '''

'''Learning Objectives'''
|| In this tutorial, we will learn to,

'''Simulate''' reflection and refraction of a light ray.

Calculate the angles of reflection and refraction.

Change the medium and '''angle of incidence''' to verify '''Snell's Law'''.

|-
|| '''Slide Number 3'''

'''Learning Objectives'''
|| Calculate the value of '''critical angle'''.

Verify '''Huygens' principle'''.

|-
|| '''Slide Number 4'''

'''System Requirements'''
|| Here I am using,

Ubuntu Linux OS version 16.04

Firefox web browser version 62.0.3
|-
|| '''Slide Number 5'''

'''Pre-requisites'''

'''https://spoken-tutorial.org/'''
|| To follow this tutorial, learner should be familiar with '''Apps on Physics'''.

For pre-requisites tutorials please visit this site.

|-
|| '''Slide Number 6'''

'''Link for Apps on physics. '''

'''https://www.walter-fendt.de/html5/phen/'''
|| Use the given link to download the '''Apps'''.

|-
|| Open the '''Downloads '''folder.
|| I have downloaded the '''Apps on Physics''' to my '''Downloads''' folder.


|-
|| '''Slide Number 7'''

'''Apps on Physics'''
|| In this tutorial, we will use,

'''Refraction of Light ''' and 

'''Reflection and Refraction of Light Waves Apps'''.


|-
|| Right-click on '''refraction_en.htm '''file.

Select the option '''Open With Firefox web Browser''' option.

Cursor on the '''App'''.
|| Right-click on '''refraction_en.htm file'''.

Select the option '''Open With Firefox web Browser.'''

'''Reflection and Refraction of Light App''' opens in the browser.

|-
|| Cursor on the interface.
|| The '''App''' shows reflection and refraction of light through a given medium.

|-
|| Point to air and water on the interface
|| The default media are air and water.

|-
|| Point to air.

Point to water.
|| Note that the medium with lesser refractive index is shown in white background.

The medium with greater refractive index is shown in blue background.

|-
|| Point to the light that has been incident.
|| Light from the top left corner, strikes the boundary surface of the two media.

|-
|| Point to both reflection and refraction angles.
|| It shows reflection and refraction.

|-
|| Point to blue angels
|| Reflection is shown by the blue coloured angle.

|-
|| Point to black and blue angles.
|| Observe that the angle of '''incidence''' and reflection are the same.

|-
|| Point to the refraction.
|| Here we see the refraction of light.

|-
|| Show the phenomena with the motion of the cursor.
|| When light travels from rarer medium to denser medium, it bends towards '''normal'''.

|-
|| Cursor on the green '''panel'''.
|| On the green '''panel''' we have a choice to change a few parameters.

|-
|| Point to the drop downs.
|| Let us reverse the two media using the drop downs.

|-
|| Click on the first drop down and change the medium to water.
|| Select '''water''' as the upper medium.

|-
|| Click on second drop down.

Select air from the drop down.
|| Select '''air''' as the lower medium.

|-
|| Move the cursor to show the movements 
|| Here the ray of light travels from denser to rarer medium.

The ray bends away from the '''normal'''.

|-
|| Click on both drop down to show the material medium.
|| Note that both the drop downs show the same material media.

|-
|| Point to each drop down.
|| Below the drop down, we see two text fields. 

These are provided to enter the values of refractive indices.

|-
|| Enter the value 4 in the '''1<sup>st</sup> index of refraction '''and show the change.
|| Here we can also change the values manually between the range of 1 to 5.

|-
|| Click on '''F5''' key on the keyboard.
|| Press '''F5''' key on the keyboard to '''refresh''' the '''App'''.

|-
|| Change the values from 0.1 degrees to 90 degrees and show the changes.

Click on '''F5''' key on the keyboard to '''refresh''' and show the default value.
|| Next '''Angle of incidence''' can be changed from 0.1 degrees to 90 degrees.

Press '''F5''' key to see the default value.

It shows 30 degrees.

|-
|| Point below the text fields.
|| Below the text fields '''App''' shows the '''Angle of reflection''' and '''refraction'''.

|-
|| Point to the graph.
|| Graph shows the angle of refraction with '''angle of incidence'''.

|-
|| Click and drag the '''angle of incidence'''.

Drag it slowly.
|| We can also change the '''angle of incidence''' by dragging this red coloured ray.

|-
|| Point and show the changes when the angle of incidence is changed.
|| Notice the change in angle of reflection and refraction.

Simultaneously observe the graph.

|-
|| Cursor on the interface.
|| Now from the graph we will learn the two cases of '''Snell’s law'''.

|-
|| '''Slide Number 8'''

'''Snell’s Law of Refraction'''

sin i / sin r = n<sub>21</sub>

“n<sub>21</sub>” is the refractive index of the second medium w.r.t first.
|| Before that let us state '''Snell’s law''' of refraction.

Ratio of '''sine''' of angle of '''incidence''' to '''sine''' of angle of '''refraction''' is a constant.

n<sub>21 </sub>is the refractive index of second medium with respect to first medium.

|-
|| '''Slide Number 9'''

'''Snell’s Law of Refraction'''

'''Case1: '''If''' '''n<sub>21 </sub>> 1, angle of refraction is less than angle of '''incidence'''.

'''Case2: '''If''' '''n<sub>21 </sub>< 1, angle of refraction is greater than angle of '''incidence'''.
|| Here are the 2 cases of '''Snell’s law'''.

1. If n<sub>21 </sub>is greater than 1, angle of refraction is less than angle of '''incidence'''.

2. If n<sub>21 </sub>is less than 1, angle of refraction is greater than angle of '''incidence'''.

|-
|| Edit the value of '''Angle of incidence''' to 20 degrees.
|| Change the '''Angle of incidence''' to 20 degrees.

Observe that the '''angle of refraction''' has changed to 14.9.

|-
|| Point to the graph and values of the angles.
|| This graph shows the first case of '''Snell’s law'''.

Here angle of '''incidence''' is greater than the 

angle of refraction.

|-
|| Point to the value of refractive index of the second medium.
|| Observe that the light ray bends towards the '''normal'''.

|-
|| Cursor on the interface.
|| Let us see what happens, when incident ray passes from denser to rarer medium.

|-
|| Click on the first drop down and change the medium to diamond.
|| From the first drop down change the material medium to '''diamond'''.

|-
|| Point to show the refraction.
|| Notice that the light ray has bent away from the '''normal'''.

|-
|| Point to the graph.
|| This graph shows the second case of '''Snell’s law'''.

|-
|| Point to show Angle of refraction.
|| Here the angle of refraction is greater than the angle of '''incidence'''.

|-
|| Change the '''Angle of incidence''' to 30 degrees.
|| Increase the '''Angle of incidence''' to 30 degrees.

|-
|| Point to the refracted ray.
|| The refracted ray has bent still more further away from the '''normal'''.

|-
|| Change the '''Angle of incidence''' to 35 degrees.
|| Again increase the '''angle of incidence''' to 35 degrees.

In this case observe that the refraction is not possible.

|-
|| Point to the reflected ray.
|| Here the incident ray is totally reflected.

|-
|| Cursor on the interface.
|| This phenomenon is known as '''total internal reflection'''.

Here the '''critical angle''' is formed.

|-
|| Point to the '''Critical angle'''.
|| The '''critical angle''' for diamond and water is 33.3 degrees.

|-
|| '''Slide Number 10'''

'''Critical angle'''

i<sub>c</sub><nowiki>= sin</nowiki><sup>-1</sup>(n<sub>2</sub>/n<sub>1</sub>)

i<sub>c</sub><nowiki>= Critical angle</nowiki>

n<sub>1</sub><nowiki>= Refractive index of first medium</nowiki>

n<sub>2</sub><nowiki>= Refractive index of the second medium</nowiki>
|| Now we will calculate the '''critical angle''' using the formula.

|-
|| '''Slide Number 11'''

'''Tabular column'''
|| Let us make a tabular column to calculate '''critical angle''' for two different media.

|-
||point to the calculated values. 
|| Here I have calculated the '''critical angle''' for diamond and water. 

|-
|| Point to the on the interface '''Critical angle'''.
|| The calculated value is comparable to the value shown in the '''App'''.

|-
|| '''Slide Number 12'''

'''Tabular column'''

|| Now enter these values in the table.

|-
|| Change the upper medium to '''water''' and lower medium to '''air'''.
|| Next change the upper medium to '''water''' and lower medium to '''air'''.

|-
|| '''Slide Number 13'''

'''Tabular Column'''

Show one glimpse of the table 
|| Note the refractive indices for both the media.

|-
|| Show the calculation of '''critical''' angle as image.
|| Then calculate the '''critical angle''' using the above formula.

|-
|| Point to show the values.
|| Observe that the values are comparable.

|-
|| '''Slide Number 14'''

'''Tabular column'''
|| Note these values in the table.

|-
|| '''Slide Number 15'''

'''Assignment '''

Show the incomplete table.
|| As an assignment 
* Note the values of refractive indices for the following media from the '''App'''.

* Calculate the '''critical angle''' for the two media.

* Compare the values with the ones shown in the '''App'''.

|-
|| Cursor on the interface.
|| Now we will move on to the next '''App'''.

|-
|| Right click on '''refractionhuygens_en.htm'''.

'''Open With Firefox Web Browser'''.
|| Right click on '''refractionhuygens_en.htm '''file.

'''Open With Firefox Web Browser'''.

The '''App''' opens in the browser.

|-
|| Highlight the main topic from the screen.
|| '''App''' shows '''Reflection''' and '''Refraction''' of light waves using '''Huygen's''' principle.

|-
|| Click on the '''Restart''' button.
|| Click on the '''Restart''' button.

|-
|| Point to the wavefront.
|| Here the '''plane wavefront''' is incident diagonally on the boundary of the media. 

|-
|| Click on the '''Next step''' button.
|| Click on the '''Next step''' button.

|-
|| Point to the box and scroll the slider.(Highlight the box)
|| Explanation of each step is provided in this text box.

|-
|| Point to the '''wavefronts'''.
|| Note the change in media, when the '''wavefront''' is incident on the boundary.

|-
|| Click on the '''Pause''' button.
|| Click on the '''Pause''' button.

|-
|| Point to the pink point on the boundary.
|| Observe the pink points on the boundary between the media.

Each pink point is the source of '''spherical wavefront'''.

|-
|| Point to the waves in '''Medium1 '''and '''Medium 2'''.
|| These generating waves in the '''Medium 1 '''and''' Medium 2''' are the wavelets.

|-
|| Click on the''' Resume''' button.
|| Click on the''' Resume''' button.

|-
|| Cursor on the interface.
|| Note that the waves in '''Medium 2''' move with less velocity as compared to '''Medium 1'''.

This is because, the '''medium 2''' has higher refractive index.

So here the waves move with less velocity.

|-
|| Click on the '''Next step''' button.
|| Click on the '''Next step''' button.

|-
|| Click on the '''Pause''' button.
|| Click on the '''Pause''' button.

|-
|| Point to the line drawn.
|| Observe the tangent drawn to all these '''spherical waves'''.

This line, here is the source for the secondary '''wavefront'''.

|-
|| Points on the wavelets.
|| So, the points on every wavelet result in the formation of secondary '''wavefront'''.

|-
|| Point to the values.
|| Here the values of '''Angle of incidence''', '''reflection '''and '''refraction '''are given.

|-
|| Click on the '''Resume''' button.
|| Click on the '''Resume''' button.

|-
|| Point and show the direction of propagation of the red and blue waves.
|| Direction of propagation changes when waves move from '''medium 1''' to '''medium 2'''. 

|-
|| Click on the '''Next step''' button.
|| Again click on the '''Next step''' button.

|-
|| Point to direction of the propagation of waves.
|| Here the direction of the propagation of waves is shown.

|-
|| Click on the '''Pause''' button.
|| Click on the '''Pause''' button.

|-
|| Point and show the perpendicular lines.
|| Observe that these lines of propagation are perpendicular to the '''wavefronts'''.

|-
|| Click on the '''Resume''' button.
|| Click on the '''Resume''' button.

|-
|| Change '''Angle of incidence '''<nowiki>= 60 degrees.</nowiki>
|| Change the '''Angle of incidence''' to 60 degrees.

|-
|| Click on the '''Next step'''.
|| Click on the '''Next step''' button.

|-
|| Point the series of waves.
|| Here we can see a series of '''wavefronts''' that are incident on the boundary surface.

|-
|| Cursor on both mediums.
|| Observe the speed and wavelength of '''wavefronts''' in both the media.

|-
|| Point to the denser medium.
|| The wavelength and speed of the '''wavefront''' decreases in the denser medium.

But the frequency of the plane '''wavefronts''' remains the same.

|-
|| make the refractive index of 1 to 2 and refractive index of 2 to 1.
|| Let us reverse the refractive indices and observe the formation of '''wavefronts'''.

|-
|| Point to the '''wavefronts'''.
|| Here the speed of the '''wavefront''' decreases, as it moves from denser medium.

|-
|| Cursor on the interface.

Point to show the critical angle.
|| This shows the total internal reflection. 

Here the incident '''wavefront''' is completely reflected and not refracted.

This results in the formation of '''critical angle'''.

|-
|| '''Slide Number 16'''

'''Assignment'''

Change the refractive index values of both media as given in the previous '''App'''.

Observe the formation of '''wavefront''' and give an explanation.

|| As an assignment

Change the refractive index values of both media as given in the previous '''App'''.

Observe the formation of '''wavefront''' and give an explanation.

|-
|| 
|| Let us summarize

|-
|| '''Slide Number 17'''

'''Summary''' 
|| Using these '''Apps''', we have

'''Simulated''' reflection and refraction of a light ray.

Calculated the angles of reflection and refraction.

Changed the medium and '''angle of incidence''' to verify '''Snell's Law'''.

|-
|| '''Slide Number 18'''

'''Summary''' 
|| Calculated the value of '''critical angle'''.

Verified '''Huygens' principle'''.


|-
|| '''Slide Number 19'''

'''Acknowledgement'''

These '''Apps''' are created by Walter-fendt and his team.
|| These '''Apps''' were created by Walter-fendt and his team.

|-
|| '''Slide Number 20'''

'''About the Spoken Tutorial project.'''



|| The video at the following link summarizes the Spoken Tutorial project.

Please download and watch it.

|-
|| '''Slide Number 21'''

'''Spoken Tutorial workshops.'''

|| The&nbsp;'''Spoken Tutorial Project&nbsp;'''team,

conducts workshops and gives certificates.

For more details, please write to us.

|-
|| '''Slide Number 22'''

'''Forum for specific questions:'''

Do you have questions in THIS Spoken Tutorial?

Please visit this site

Choose the minute and second where you have the question. 

Explain your question briefly.

Someone from our team will answer them.
|| Please post your timed queries in this forum.

|-
|| '''Slide Number 23'''

'''Acknowledgement'''
|| Spoken Tutorial Project is funded by MHRD Government of India.

|-
|| 
|| This is Himanshi Karwanje from IIT Bombay 

Thank you for joining.

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|}